Nanotubes are small tubular structures that are conventionally formed primarily from covalently bonded carbon atoms, although nanotubes formed of other materials (e.g., gallium nitride, boron nitride, carbon nitride, and transition metal sulfides, selenides, halogenides, and oxides) have also been produced. Nanotubes are a relatively recently discovered form of matter. Since their discovery, nanotubes have been formed having various diameters, lengths, compositions, and structural forms (i.e., chirality, or twist). The physical, electronic, and thermal properties that may be exhibited by nanotubes vary broadly and are at least partially a function of one or more of the size, composition, and structure of the nanotubes. For example, nanotubes may be electrically conductive, semiconductive, or nonconductive.
Nanotubes may be formed as so-called single wall nanotubes (SWNTs), or they may be formed as so-called multiple wall nanotubes (MWNTs). Single wall nanotubes have a single wall of covalently bonded atoms, whereas multiple wall nanotubes include two or more generally concentric walls of covalently bonded atoms. Multiple wall nanotubes may be visualized as one or more nanotubes positioned within another nanotube.
Various techniques may be used to fabricate nanotubes including, for example, chemical vapor deposition (CVD) methods, arc discharge methods, and laser ablation methods. A background discussion of carbon nanotubes, as well as methods for fabricating nanotubes can be found in, for example, Dresselhaus et al., Carbon Nanotubes: Synthesis, Structure, Properties, and Applications, Topics Appl. Phys., vol. 80, pp. 1-109 (Springer 2001), the disclosure of which is incorporated herein in its entirety by this reference.
It is known that some physical properties of nanotubes vary with mechanical deformation. For example, it has been shown that the electrical resistance of a carbon nanotube varies when mechanical deformation (i.e., strain) is induced in the carbon nanotube. See, for example, R. Ciocan et al., Determination of the Bending Modulus of an Individual Multiwall Carbon Nanotube Using an Electric Harmonic Detection of Resonance Technique, Nano Letters, vol. 5, no. 12, 2389-2393 (2005), C. Stampfer et al., Nano-Electromechanical Displacement Sensing Based on Single-Walled Carbon Nanotubes, Nano Letters, vol. 6, no. 7, 1449-1453 (2006), the disclosure of each of which is incorporated herein in its entirety by this reference. Furthermore, it has been proposed in the art to employ nanotubes in sensor devices. See, for example, United States Patent Application Publication No. 2004/0004485 A1, published Jan. 8, 2004, United States Patent Application Publication No. 2006/0010996 A1, published Jan. 19, 2006, and United States Patent Application Publication No. 2006/0283262 A1, published Dec. 21, 2006, the disclosure of each of which is also incorporated herein in its entirety by this reference.
There remains a need in the art for sensors, transducers, and other devices that employ the unique characteristics and properties of nanotubes in other and further applications, and for methods of making and using such devices.